This invention relates to a process for producing a magnetic recording material comprising aluminum or an aluminum alloy on the surface of which a magnetic recording layer having an increased magnetic intensity is formed, and which is suitable for use in a computer, a magnetic disc for a video, a magnetic sheet, etc., and to the magnetic recording material obtained by such process.
Several proposals have been heretofore made concerning magnetic recording materials made of aluminum or aluminum alloys. For example, U.S. Pat. No. 4,109,287 discloses a magnetic recording material comprising aluminum or aluminum alloy on the surface of which a film having a great number of micropores is formed by an anodic oxidation treatment, each of the micropores being substantially completely filled with a magnetic substance by an electrolytic treatment in an electrolyte containing dissolved therein a salt of the magnetic substance.
As is well known, an anodic oxide film on the surface of aluminum or aluminum alloys which is formed by an anodic oxidation treatment consists of a porous layer and a barrier layer. The porous layer occupying the major portion of the film has a great number of elongated micropores which extend in the direction perpendicular to the surface of the base metal and are arranged closely and relatively uniformly at a minute distance from each other. The thin barrier layer lies between the bottom of the micropore and the base metal. The film generally has excellent hardness, wear resistance, adhesiveness, and other desirable characterisitcs.
Therefore, when the micropores are filled with a magnetic substance, it is densely and relatively uniformly introduced. The resultant magnetic recording material is capable of high density recording and also has other excellent magnetic characteristics.
Furthermore, Japanese Pat. No. 1079289 (Japanese Examined Patent Publication No. 56-23207) proposes further anodic oxidation of aluminum or aluminum alloy on the surface of which an anodic oxide film is formed by an anodic oxidation treatment in an acidic bath in order to enlarge the pore diameter of the micropores in the film, thereby causing a magnetic substance to be deposited in the resultant micropores in a larger amount.
In accordance with this proposal, it is possible to obtain a magnetic recording material having an increased amount of the magnetic substance deposited in the micropores and exhibiting an increased magnetic intensity. However, the barrier layer lying between the micropores and the base metal is not uniform in thickness, and, thus, the lengths of the micropores are not uniform. In addition, the cross section of each micropore has a jagged profile, for example, a star-shaped profile. Therefore, this magnetic recording material leaves something to be desired with respect to the pore diameter of the micropores. When magnetic recording is carried out by using this magnetic recording material, the squareness ratio, i.e., intensity of residual magnetization/intensity of saturated magnetization, of the magnetic hysteresis is poor.